Re: mdadm --assemble considers event count for spares

[NeilBrown <neilb@suse.de>]

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On Mon, 27 May 2013 13:05:34 +0300 Alexander Lyakas <alex.bolshoy@gmail.com>
wrote:

> Hi Neil,
> It can happen that a spare has a higher event count than a in-array drive.
> For exampe: RAID1 with two drives is rebuilding one of the drives.
> Then the "good" drive fails. As a result, MD stops the rebuild and
> ejects the rebuilding drive from the array. The failed drive stays in
> the array, because RAID1 never ejects the last drive. However, the
> "good" drive fails all IOs, so the ejected drive has a larger event
> count now.
> Now if MD is stopped and re-assembled, mdadm considers the spare drive
> as the chosen one:
> 
> root@vc:/mnt/work/alex/mdadm-neil# ./mdadm --assemble /dev/md200
> --name=alex --config=none --homehost=vc --run --auto=md --metadata=1.2
> --verbose --verbose /dev/sdc2 /dev/sdd2
> mdadm: looking for devices for /dev/md200
> mdadm: /dev/sdc2 is identified as a member of /dev/md200, slot 0.
> mdadm: /dev/sdd2 is identified as a member of /dev/md200, slot -1.
> mdadm: added /dev/sdc2 to /dev/md200 as 0 (possibly out of date)
> mdadm: no uptodate device for slot 2 of /dev/md200
> mdadm: added /dev/sdd2 to /dev/md200 as -1
> mdadm: failed to RUN_ARRAY /dev/md200: Input/output error
> mdadm: Not enough devices to start the array.
> 
> Kernel doesn't accept the non-spare drive considering it as non-fresh:
> May 27 12:42:28 vsa-00000505-vc-0 kernel: [343203.679396] md: md200 stopped.
> May 27 12:42:28 vsa-00000505-vc-0 kernel: [343203.686870] md: bind<sdc2>
> May 27 12:42:28 vsa-00000505-vc-0 kernel: [343203.687623] md: bind<sdd2>
> May 27 12:42:28 vsa-00000505-vc-0 kernel: [343203.687675] md: kicking
> non-fresh sdc2 from array!
> May 27 12:42:28 vsa-00000505-vc-0 kernel: [343203.687680] md: unbind<sdc2>
> May 27 12:42:28 vsa-00000505-vc-0 kernel: [343203.687683] md: export_rdev(sdc2)
> May 27 12:42:28 vsa-00000505-vc-0 kernel: [343203.693574]
> md/raid1:md200: active with 0 out of 2 mirrors
> May 27 12:42:28 vsa-00000505-vc-0 kernel: [343203.693583] md200:
> failed to create bitmap (-5)
> 
> This happens with the latest mdadm from git, and kernel 3.8.2.
> 
> Is this the expected behavior?

I hadn't thought about it.

> Maybe mdadm should not consider spares at all for its "chosen_drive"
> logic, and perhaps not try to add them to the kernel?

Probably not, no.

NeilBrown



> 
> Superblocks of both drives:
> sdc2 - the "good" drive:
> /dev/sdc2:
>           Magic : a92b4efc
>         Version : 1.2
>     Feature Map : 0x1
>      Array UUID : 8e051cc5:c536d16e:72b413fa:e7049d4b
>            Name : zadara_vc:alex
>   Creation Time : Mon May 27 11:33:50 2013
>      Raid Level : raid1
>    Raid Devices : 2
> 
>  Avail Dev Size : 975063127 (464.95 GiB 499.23 GB)
>      Array Size : 209715200 (200.00 GiB 214.75 GB)
>   Used Dev Size : 419430400 (200.00 GiB 214.75 GB)
>     Data Offset : 2048 sectors
>    Super Offset : 8 sectors
>    Unused Space : before=1968 sectors, after=555632727 sectors
>           State : clean
>     Device UUID : 1f661ca3:fdc8b887:8d3638ab:f2cc0a40
> 
> Internal Bitmap : 8 sectors from superblock
>     Update Time : Mon May 27 11:34:57 2013
>        Checksum : 72a97357 - correct
>          Events : 9
> 
> sdd2 - the "rebuilding" drive:
> /dev/sdd2:
>           Magic : a92b4efc
>         Version : 1.2
>     Feature Map : 0x1
>      Array UUID : 8e051cc5:c536d16e:72b413fa:e7049d4b
>            Name : zadara_vc:alex
>   Creation Time : Mon May 27 11:33:50 2013
>      Raid Level : raid1
>    Raid Devices : 2
> 
>  Avail Dev Size : 976123417 (465.45 GiB 499.78 GB)
>      Array Size : 209715200 (200.00 GiB 214.75 GB)
>   Used Dev Size : 419430400 (200.00 GiB 214.75 GB)
>     Data Offset : 2048 sectors
>    Super Offset : 8 sectors
>    Unused Space : before=1968 sectors, after=556693017 sectors
>           State : clean
>     Device UUID : 9abc7fa9:6bf95a51:51f2cd65:14232e81
> 
> Internal Bitmap : 8 sectors from superblock
>     Update Time : Mon May 27 11:35:56 2013
>        Checksum : 3e793a34 - correct
>          Events : 26
> 
> 
>    Device Role : spare
>    Array State : A. ('A' == active, '.' == missing, 'R' == replacing)
> 
> 
> Thanks,
> Alex.


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